Use of renewable feed stocks for production of transportation fuels as a substitute to depleting fossil fuel is increasing [D. L. Klass, Academic Press, 1998, San Diego; L. R. Lynd, J. H. Cushman, R. J. Nichols, and C. E. Wyman, Science., 251 (1991) 1318-1323; C. E. Wyman, Appl. Biochem. Biotechnol., 45-46 (1994) 897-915]. European Union targets 2050 to use maximum biofuel in transportation fuel. Asian countries have also set a target of 20% blending of bio-fuels by 2020. Biofuels account for 9% of global transport fuels by 2030 with their production expected to increase three and half times from 1.8 millionbarrels/day (mbpd) in 2010 to 6.7 mbpd by 2030. Vegetable oils are renewable resources currently being used for production of biofuels from sustainable biomass feed stocks. There are many benefits of biofuels apart from use as domestic fuels like decrease in greenhouse gas emissions, dependence on fossil fuels, enhancing rural economy and increased national security [G. W. Huber, S. Iborra, A. Corma, Chem. Rev. 106 (2006) 4044; D. L. Klass, Biomass for Renewable Energy, Fuels and Chemicals, Academic Press, San Diego, 1998: L. R. Lynd, J. H. Cushman, R. J. Nichols, C. E. Wyman, Science 251 (1991) 1318]. Biodiesel production from trans-esterification of vegetable oils is currently the primary route for production of biofuels from vegetable oils. This process has many benefits; however, new biodiesel plants must be built requiring a capital investment. The economics of biodiesel production depends on selling the by-product glycerol, and increasing biodiesel production will cause the price for glycerol to decrease. Other alternatives for biofuels production are hydro processing of vegetable oils. One advantage for this process is to use existing petroleum refineries configuration for the process. There is no problem of glycerol production and its disposal.
In refining industry hydro-treating is used to remove S, N and metals from petroleum-derived feed stocks including heavy gas-oil or vacuum gas-oil. Vegetable oil hydro-treating produces straight chain alkanes ranging from n-C15-n-C18 which have a high cetane number ranging from 75-98, whereas typical diesel fuel has a cetane number around 45. The normal alkanes produced also have better cold flow properties. Commercial road trial of six postal delivery vans for a period of ten months showed that engine fuel economy was greatly improved by 20% blend of hydro-treated tall oil with diesel [M. Stumborg, A. Wong, E. Hogan, Bioresour. Technol. 56 (1996) 13]. The advantages of hydro-treated vegetable oil over trans-esterification resulted in switch over from fossil fuel to vegetable oil without any hardware modification in refinery and motor engine in transportation sector [M. Stumborg, A. Wong, E. Hogan, Bioresour. Technol. 56 (1996) 13]. Neste Oil Corporation is currently adding 3500 barrels per day unit to their Porvoo Kilpilahti, Finland oil-refinery that produces diesel fuel from vegetable oil by a modified hydro-treating process [Neste Oil, Neste Oil (2006), http://www.nesteoil.com/ (access year 2007)]. To process vegetable oil in existing petroleum refinery using existing infrastructure the vegetable oils need to be co-processed with petroleum-derived feed stocks such as heavy vacuum oil (HVO).
U.S. Pat. No. 4,992,605 describes vegetable oils conversion to diesel by using sulfided Ni—Mo and Co—Mo catalysts in presence of high hydrogen pressures (5-15 MPa) and temperatures in the range of 350 to 450° C. The vegetable oils such as soya, palm and sun flower were used as bio-feed. At low temperatures the yield does not meet the specifications. U.S. Pat. No. 5,233,109 describes thermal and catalytic cracking of vegetable oils leading to a wide range of products such as paraffins, aromatics and unsaturated hydrocarbons in the boiling range of gasoline and gas oils. The method described produces derivatives that cannot be directly used as gas oil fuel bases because the derivatives do not meet specifications like oxidation stability. Different catalysts used for the conversion are Akzo Ketjen Vison-47, Zeolite X, silica gel and Fluka alumina. Present invention describes hydro-treating of vegetable oils which differ from pure cracking.
U.S. Pat. No. 7,781,629 teaches a hydro-treating method where two catalyst beds are used by dedicating first one for only hydrodesulphurization whereas the second one is used for treating some part of the conventional gas oil and vegetable oils together. The effluents obtained at the out let of the second catalyst bed can be mixed with the predominant stream from the first bed. By following this method the process economy and specifications of the products were greatly met. Co—Mo and Ni—Mo catalysts have been used in the process but concentrations of metals have not been provided. This patent mainly focuses on process.
U.S. Pat. Nos. 4,992,605 and 5,705,722 describe methods of producing bio diesel from direct conversion of vegetable oils (rape, palm, soybean, and sunflower) or of lignocellulosic biomass to saturated hydrocarbons after hydro-treatment or hydro-refining of these products. The conversion methods described are operated at temperatures ranging from 350° C. and 450° C. to yield products with a high cetane number. In the proposed invention reactions were carried out at moderate hydrogen pressures and relatively low hydrogen consumption. The high cetane additives thus obtained are mixed with gas oil in proportions of 5 to 30% by volume. These two patents have the major drawback of high hydrogen consumption essentially due to the unsaturations present in the feeds consisting of vegetable oils and to the fact that the oxygen contained in the triglycerides is generally decomposed by hydro-deoxygenation in the presence of a hydro-treating catalyst. In the U.S. Pat. No. 5,705,722, a commercial nickel-molybdenum or alumina catalyst available under the trade mark CRITERION 424, was supplied in the form of extrudates (used for vegetable oil conversion).
U.S. Pat. No. 0,260,102 A1 describes a process wherein vegetable oils are converted to paraffins, wherein vegetable oils are hydro-treated as such or in combination with mineral hydrocarbon oil. This patent also concentrates in producing the n-paraffins which are raw materials for the production of detergents (LAB) which is beneficial for using in situations where kerosene is limiting factor for producing n-paraffins.
U.S. Pat. No. 2,163,563 teaches a method for conversion of vegetable oils and mineral oil mixtures in presence of hydrogen at high pressures (5-50 Mpa) using reduced nickel catalysts supported on alumina.
U.S. Pat. No. 4,300,009 teaches a catalytic conversion method wherein vegetable oils are converted to gasoline range molecules by using large pore zeolites preferably more than 5 Å.
Efficient utilization of biomass for the production of transportation fuels such as biodiesel is becoming increasingly important. In future, bio fuels may replace the gasoline and diesel requirements across the world. Present use of biofuels as blend can slow down the consumption of petroleum products while preserving the oil reserves.
Biodiesel is an alternate transportation fuel mainly produced by trans-esterification of vegetable oils. In trans-esterification process, large amount of water or methanol is used and large quantities of by-product glycerol are produced. In addition, the oxidation stability of the biodiesel is poor; and the engine may need some modifications or special maintenance when methyl esters are used. Moreover new plants are required to be built. The refinery hydro processing technology which is used for diesel or Vacuum Gas Oil (VGO) hydro-treating is one answer to address the above discussed drawbacks of trans-esterification process. The basic idea is to mix the VGO stream with vegetable oil and by effect of a high pressure, high temperature and a bi-functional catalyst; the triglycerides in the oil are transformed into hydrocarbons in the diesel range.
Not withstanding the amount of material available in the literature, there is a continuous need in this field of technology to provide an improved catalyst and process for conversion of vegetable oils to diesel at high temperatures and high hydrogen pressures. The catalyst should be more efficient in full conversion of vegetable oils. The catalyst should be able to retain the catalyst activity for longer durations and the products should meet al requisite specifications to use as transportation fuels.
Present invention concentrates on development of new catalyst formulations for vegetable oil conversion to diesel. The present invention concentrates in generation of diesel range molecules rather than gasoline range molecules. The catalyst composition of the present invention differs in constitution, product properties, efficiency and reaction conditions from the catalyst compositions of the prior art.